My understanding.
-- There is the core. Metal. Contains the rods. Water in here turns to steam and goes to primary heat exchanger then secondary which sends steam to turbines.
-- Containment structure. Concrete "bucket" to hold the core if it melts. Usually empty bucket, but they flushed it with water. (Also filled core with H20 after releasing H2.)
-- Outer structure of building. Square, pixillated. t

I live near a nuclear power plant in the States, built to a similar design. As I understand it, it's a bit more "complicated" than what you described.

From the one tour a few years back with the school I was doing my student teaching at, if I remember properly it's more something like:

--Core. Made of between six inches and one foot of steel. This is where the control rods are kept and partitioned off with either graphite or zirconium. There is also a heavy (several hundred ton) metal cap on top of this. It is removed during refurbishing the interior systems. Leading into this are a handful of emergency shut down pipes that can (if need be) dump borax or even sea water into the system to force it to shut down. Doing this is called scramming and is permanent. There are also a number of coolant lines which keep the reactor from overheating.
--Steam lines. Surrounding the central core, a number of lines circle which pull water in and send steam out. These steam lines usually travel to the generator room which is located a short distance away, before passing through the cooling towers to condense the water. It is then either re-used or dumped into the ecosystem.
--Exterior containment: First line of containment, consisting of a concrete shell around the steam lines. Between one and two feet thick, with a concrete cap on average three feet thick at the top.
--Exterior shielding. Depends on the type of reactor, can be water, though in most cases it is just more concrete with lead interspersed in it to absorb any radiation.

The above constitute the "Reactor" itself. This Reactor is then contained in a building structure itself. In the Japanese design, spent fuel is kept in water pools above the reactor. These pools are between 20 and 30 feet deep and will hold the spent fuel until it can be disposed of. (Disposal is done by sinking the spent fuel in concrete blocks and burying it under miles of earth.)

In the case of Chernobyl, the reactor design did not allow for a fast scramming, so when the reaction screwed up, it started to produce vast amounts of steam as it boiled off the coolant being pumped into the reactor vessel. As the steam built up more and more pressure; eventually the top of the reactor gave way, blowing the reactor cap up and off. Not long after this, (some accounts say about 3 seconds) the fissionable material inside the reactor went critical and detonated with the force equal to that of the Hiroshima bomb. The resulting cloud sent material and dust into the air, with the largest chunk of control rod material being found some six miles away from the blast.

That is putting it mildly. As it stands, the entire of the Japanese navy was provided by the United States. They have the super advanced Aegis system, as well as look down shoot down missile systems; and an over the horizon anti ship and anti submarine system that is on par with the US. Japan is one of the few nations to actually have the nuclear depth charges. The JMSDF's submarine fleet also consists of one of the most technologically advanced and capable diesel-electric forces in the world. This is due to careful defense planning in which boats are routinely retired ahead of schedule and replaced by increasingly advanced models.

The scary thing is, Diesel Subs though limited in use on the surface, are actually quieter under water than nuclear powered submarines. Meaning that any attack against Japan by the US would be VERY costly for the US navy.

In the plan, Japs are supposed to fight against Chineses besides Americans.

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1751: Daniel Kahl tweets: "Tokyo is a ghost town tonight. No people on the streets. Even the entertainment districts. Eerily quiet. But Tokyo is amazing. Even with blackouts, train problems, no rioting, no looting, no robberies."BBC News - LIVE: Japan earthquake

Why looting for radiactively contaminated stuff when you know that at some point you'll have to rush to flee the region ?